I keep saying what Brock and snip have said. An R Class battleship is nothing to take lightly. Had it been refitted with modern DP secondaries, radar and perhaps some new engines and additional deck armour it would be a powerful ship. But, I agree Imperial is slow and old and badly dated in her original form as she currently exists.
I don't like the concept of 'pocket' battleships, they don't exist, they are heavy cruisers with bigger than Washington limit guns. Nothing more, nothing less. The Pazerschiff were a reaction to a particular set of treaty restrictions. The later P-1 class that were never built were more akin to battlecruisers. The Imperial is a dreadnought, plain and simple. I toyed with 12in armed monitors for Argentina several times but really the cost was unjustifiable for glorified coastal defence ships. A couple of modern battleships built with old 15in guns would make more sense in the long term.